The present invention relates to graphic plotters and, more particularly, to a turret head carriage assembly for a graphics plotter which provided a plurality of pens immediately adjacent the point of writing.
Computer graphics is a rapidly expanding technology. The requirements of computer aided design, computer aided engineering, and computer aided manufacture have precipitated the ability to create and display complicated graphics materials. Correspondingly, there has been a rapid increase in the requirements placed upon graphics plotters to create tangible drawings of the displayed graphics for use in the manufacturing process. For one thing, a single pen to be manually changed is not sufficient for most high level applications. With multi-color representations, the pens must be exchanged to create the different colors. Similarly, with liquid ink pens used to create engineering drawings, the pens must be exchanged to get different sized tips thereon for making different width lines as required in various portions of the drawing. Thus, the ability to have automated pen exchanging within the graphics plotter itself has long been a need which, of recent times, has increased in its restrictions.
Several approaches have been employed in the prior art. One example is shown in FIGS. 1-5 wherein the plotter 10 has a movable arm 12 which moves back and forth in the direction of arrows 14 while a movable pen carriage 16 containing gripping fingers 18 to hold a pen 20 moves across the arm 12 in the direction of arrows 22 to create the plot 24 on the writing medium 26. A holding station, generally indicated as 28, is provided adjacent the edge of the plotter 10 and comprises a plurality of adjacent gripping fingers 18, holding pens 20 to be exchanged. To effect a change of pen using the prior art apparatus of FIGS. 1-5, the sequence shown therein must be accomplished. First, the arm 12 and carriage 16 have to leave the point of writing 30 and return the pen 20 in gripping fingers 18 on carriage 16 back to the empty position of holding station 28 as shown in FIG. 2. They then move to the selected pen 20 at holding station 28 as shown in FIG. 3 where the new pen 20 is picked up. Arm 12 and carriage 16 then return to the point of writing 30 as shown in FIG. 4 whereupon the plot 24 can be continued as shown in FIG. 5.
As can be realized, such a pen exchange routine where the pen being used must be moved from the point of writing to a remote location for the exchange and the new pen return before plotting continues is very time consuming. One way that the prior art has attempted to solve this is by the use of a pen carriage having a turret head such as that indicated as 32 in FIGS. 6 and 7. In such prior art devices, the movable pen carriage 16 on the movable arm 12 is provided with a turret head 32 having a central portion 34 rotatable about a central shaft 36 as with a stepping motor (not shown). About the central portion 34 are disposed a plurality of writing stations 38, each configured as shown in FIGS. 8 and 9. The writing stations 38 each comprise a solenoid type arrangement wherein the pen 20 is contained within a movable armature housing 40 within a coil 42 and held in the raised position as with coil spring 44. Assuming the writing station 38 labeled "0" is the active point of writing, to use the pen in writing station 38 labeled " 2", the entire central portion 34 and all the writing stations 38 are rotated from the position of FIG. 6 to the FIG. 7. The coil 42 of the writing station 38 at location "2" is then activated by the application of current to the wires 46 of coil 42 causing the armature 40 to be drawn downward against the bias force of spring 44 to place the tip 48 of pen 20 in contact with the writing medium. As will be appreciated, since each writing station 38 has a coil 42 and armature 40, the total weight of the turret head 32 can become quite large. Accordingly, the turret head 32 possesses a high inertia. In very large, very expensive graphic plotters, such weight and its attendant inertia was not a major factor.
Recently, however, small-sized, low-cost personal computers have been introduced into the technical marketplace to perform high quality work. Because of their low cost, they can be afforded by many individuals and small businesses who could not otherwise afford computer capability and have, therefore, gained rapid acceptance. Accordingly, the peripherals, including the graphics plotters, have had to effect a similar reduction in cost and size in order to remain competitive. For the home enthusiast, it has been possible to accomplish the production of a low-cost, multi-pen plotter by using felt tipped pens as the writing medium. For high-quality drafting applications, however, traditional liquid ink type pens to produce India ink drawings on Mylar or other suitable writing mediums are required. To use such a drafting type pen, the plotter literally must be designed around the existing standard structure of the writing tip. To employ liquid ink type drafting pens in a configuration such as that of FIGS. 6 and 7, or by putting, for example, eight individually activated writing stations such as that shown in FIGS. 8 and 9 in an in-line configuration produces a writing head which is both large and cumbersome, as well as overweight and with a high inertia, unable to operate within a lightweight, low-cost environment.
Wherefore, it is the object of the present invention to provide a turret head assembly for use in a graphics plotter which will hold a plurality of liquid ink drafting type writing pens while being small in size and low in weight/inertia.